| # Copyright 2024 The Chromium Authors |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| import collections |
| |
| |
| class LRUMapping(collections.abc.MutableMapping): |
| """A mapping with at most N most recently used entries. Not threadsafe.""" |
| |
| def __init__(self, capacity: int): |
| # Most recently used entries are first. |
| self._inner = collections.OrderedDict() |
| self.capacity = capacity |
| |
| @property |
| def capacity(self) -> int: |
| return self._capacity |
| |
| @capacity.setter |
| def capacity(self, n: int): |
| if n < 0: |
| raise ValueError(f'capacity must be nonnegative, but was {n}') |
| self._capacity = n |
| |
| def __getitem__(self, key): |
| self._inner.move_to_end(key, last=False) |
| return self._inner[key] |
| |
| def __setitem__(self, key, value): |
| self._inner[key] = value |
| self._inner.move_to_end(key, last=False) |
| self._maybe_truncate() |
| |
| def __delitem__(self, key): |
| del self._inner[key] |
| |
| def __iter__(self): |
| return iter(self._inner) |
| |
| def __len__(self) -> int: |
| return len(self._inner) |
| |
| def _maybe_truncate(self): |
| while len(self._inner) > self._capacity: |
| self._inner.popitem() |
